Originally, naturally available and relatively light materials, such as wood, were the most common materials used for constructing aircraft. However, with the development of new alloys the aircraft construction industry shifted from one of carpentry to one of metal shaping.
Relatively recently, a new generation of materials known as “composites” or “composite materials” were developed. Certain composite materials often provide an excellent strength-to-weight ratio as compared to metals, and their acceptance into the various aircraft industries is near universal.
Generally, there are two major genres of composite materials: honeycomb structures and laminates. Honeycomb structures are exceeding light materials that provide unequalled structural support (for their weight) when placed in wings and other strategic locations in a given aircraft. Laminate materials, while usually not as light as honeycomb structures, are often lighter than any commercially viable metal equivalent, and typically far stronger than any honeycomb structure.
As with all materials, laminates are subject to damage from abuse and high-speed impacts. Unfortunately, the true extent of any resultant damage of a high-speed impact can not always be seen. That is, there are often instances where an impact to a laminate-type structure may only superficially mar its surface, but nonetheless result in extensive damage deep in the laminate's structure where it can not be readily detected. While various diagnostic tools, such as ultrasonic imagers, are available to assess such hidden damage, these existing tools can be very expensive and require a substantial amount of training to properly use. Accordingly, new methods and systems for detecting damage in laminate structures are desirable.